In an aircraft design, a continuous flow of hot air is bled from one part of a gas turbine engine, cooled, and provided to a specific user application. A heat exchanger system may be used to cool the hot bleed air.
The preferred medium for cooling hot bleed air is engine bypass air that flows through the gas turbine fan duct. There are several limitations on the design of the heat exchanger system that exchanges heat between the bleed air and the bypass air. The inlet manifold that brings the hot bleed air to the heat exchanger, the heat exchanger itself, and the outlet manifold that transports the cooled bleed air away from the heat exchanger cannot together impose too great a pressure drop, or the cooled bleed air that reaches the user application will have insufficient pressure to perform properly. Weight and size also impose tight limitations. As with all aircraft structures, it is important to keep the weight of heat exchanger system as low as possible. The heat exchanger system also cannot significantly increase the envelope size of the gas turbine engine, and desirably is as small as possible to leave installation space for other aircraft systems.
Dimensional changes are potentially a concern in the heat exchanger. The dimensional changes result from two sources. The components of the engine change size due to the mechanical loadings that occur as the gas turbine engine is powered. The components of the engine also change size as their temperatures vary during use. These dimensional changes must be accounted for in the heat exchanger structure, or otherwise the resulting stresses and strains would lead to premature failure of the heat exchanger unit. The thermally induced stresses and strains are particularly a concern for the heat exchanger system, where gases of different temperatures are in close proximity, and the relative temperature of the gases changes over time.
There is a need for a compact, lightweight heat exchanger system that cools the flow of hot bleed air.